Corrosion testing probe



Dec. 16, 1958 E. SCHASCHL CORROSION TESTING PROBE Filed Dec. 19, 1956 Kmmm mm m? INVENTOR.

EDWARD SCHASCHL BYfZ ATTORNEY United States CORROSION TESTING PROBEEdward Schaschl, Crystal Lake, Ill., assignor to The Pure Oil Company,Chicago, 111., a corporation of Ohio Application December 19, 1956,Serial No. 629,365

7 Claims. (Cl. 73-86) der pressure. whereby there is no necessity forreleasing the pressure in the vesssel or pipe during such insertion orwithdrawal. The invention lies particularly in the arrangement ofpressure seals around the lugs holding the corrosion-test specimenswithin a base member, the arrangement of the test probe as a unit withcooperating external seals and the relationship of these parts to eachother and to other parts, as will be described.

Previous designs of corrosion-test probes have necessitated relievingthe pressure in the vessel or pipe in which the probe is to be installedbefore the probe is introduced or withdrawn. This is frequentlyimpractical or impossible when it is desired to conduct a corrosionstudy on a process or pipeline, or other confined space that normallyoperates under pressure, where such vessels or pipes are designated forcontinuous and uninterrupted service over long periods of time. To shutdown a large refinery unit or a pipeline supply or other process unitsimply for the purpose of installing or removing a corrosion test probeis not economically feasible. Test probes of this type must be of ruggedconstruction yet at the same time be responsive to a wide range ofcorrosive conditions both as to the extremes in rates of corrosionencountered and as to the variations in temperature and pressure thatmay be present during the test period.

The correct sealing of a plurality of electrical leads in spaced,insulated relationship in a manner to withstand high pressure andtemperature conditions, and variations thereof, while at the same timeproviding for proper exposure of the test specimens to the corrosiveatmosphere, presents a unique problem. Also, to prepare a unit holderfor the test specimens which can be easily inserted into a pressurizedzone without danger to the operator or damage to the equipment isanother problem solved by this invention.

Direct observation of the influence of corrosion under actual serviceconditions whereby advantage is taken of the heterogeneity of thecorrosive environment is one of the most practical methods of corrosionmeasurement.

' Metallic test specimens may be simply suspended on a hanger or bymeans of a multi-unit support for a number of test specimens ininsulated relationship to exclude galvanic contacts. But such methods donot provide means for performing corrosion tests in inaccessible placesor in pressurized environments, and require tedious weighing andre-weighing of the test specimens to determine the extent and rate ofcorrosion. Furthermore, the results found from weight-loss methods aresubject to errors and a large number of specimens are necessary todetermine a proper time-corrosion curve.

Accordingly, this invention takes advantage of the methods that havebeen devised which make use of the correlation between change inelectrical conductivity and change in cross-sectional area to determinethe rate of corrosion of various materials of construction throughatent' O 2,864,252 Patented Dec. 16

the use of corrosion-test probes connected to electricalresistance-change meters. These instruments, known and widely used inthe art, employ resistance bridges and function like analogue computersto indicate quantitatively the changes in physical characteristics whichcannot be conveniently measured by other methods. There are severalrecent modifications of this principle. One such modification isdescribed in a co-pending application entitled, Apparatus forDetermining the Influence of Corrosion on Metallic Materials ofConstruction, bearing Serial Number 528,032, filed August 12*, 1955, G.A. Marsh and the present inventor. Application Serial Number 528,032describes means for compensating for temperature changes wherein onetest specimen is mounted in exposed condition to the. corrosiveatmosphere and another test specimen is insulated or protected from thecorrosive atmosphere by means of a suitable protective coating placedthereon. The coupons or test specimens are connected in a circuit so asto comprise one-half of a typical resistance bridge. Suitable electricalconnections are made With the other half of the bridge, which is placedoutside the corrosive environment along with the power supply to thebridge, and an appropriate electrical meter, such as a galvanometer,functions as a null detector. Loss of metal on the unprotected specimeninduces small increases in resistance in the circuit which arecorrelated with metal loss by appropriate formulae described in theapplication.

In another co-pending application entitled, Electronic Resistance-ChangeMeter, Serial Number 528,061, filed August 12, 1955, by Lynn E. Ellison,now Patent No. 2,830,265, there is described an electronic apparatus forconveniently detecting and measuring changes in resistance whichprovides for direct reading of the rate of corrosion. The corrosion testprobe of the present invention may be used in conjunction with theapparatus described in the foregoing applications. In still anotherco-pending application by the present inventor entitled, ImprovedCorrosion Test Probes for Use With Corosion Testing Apparatus, filedMarch 1, 1956, and bearing Serial Number 568,906, there are describedcorrosion test probes of increased rigidity, durability and strength.These probes comprise a non-conducting specimen holder which may be inthe form of a ceramic core having test specimens attached to the surfacethereof by electrolytic deposition or painted circuit methods. Thecorrosion test probe of this invention is in part an improvement overthe test probes previously proposed in that it is adapted to be usedboth under conditions of high pressure and temperature and also adaptedto be connected and disconnected from the corrosive environment withoutthe necessity of relieving the pressure conditions therein.

It becomes therefore a primary object of this invention to provide acorrosion-test probe to be used with an electronic resistance-measuringapparatus adapted to determine the corrosivity of environments underconditions of relatively high temperature and high pressure.

Another object of this invention is to provide a new form ofcorrosion-test probe having a simplified pressure seal both for the testprobe holder and the entire assembly.

Another object of the invention is to provide a corrosion-test probehousing and associated parts which allow the use of leads or conductorsfor the associated test specimens which are large enough so as to have anegligible resistance.

Still another object of the invention is to provide a corrosion-testprobe wherein the overall dimensions thereof are small enough to be usedwith the ordinary valves and conduits which are used in processingapparatus.

These and other objects of the invention will become asegeee 3 apparentor be described as the invention is set forth.

The invention is best described by reference to the attached drawings inwhich:

Figure lis a exploded isometric view of one form of test probe showingthe relationship or arts which comprise the test probe assembly.

Figure 2 is an end view of the base member used to house the lugs whichhold the corrosion test specimens as shown in Figure 1.

Figure 3 is a partial cross-sectional view of the base membertaken alonglines 3-3 of Figure 2.

Figure 4 is an enlarged, fragmentary, cross-sectional view of thesealingarrangement shown in Figure 3. Figure 5 is a partialcross-sectional view showing the means for inserting, holding andremoving the assembled corrosion-test probe into the wall of a processvesselor pipe containing the corrosive atmosphere to be tested.

I, ef erring to the drawings, particularly Figure 1, 1%

represents the exposed test specimen or strip and 12 the protected testspecimen. Specimens 10 and 12 are joined at common point or juncture 14from which center lead or tap 16 extends. The test specimens and centertap are each held by means of lugs as indicated at 17, 18 and 20 and areeach connected to leads 22, 24 and 26, respectively, which run throughthe entire assembly. The test specimens, center tap and leads may besoldered or welded to the corresponding ends of the lugs. Lugs 17, 18and 20 are identical, each comprising primary cylindrical sections 28,30 and 32 and smaller concentric cylindrical sections 34, 36, and 38.Nos. 40, 42 and 44 represent annular or rings on the outside of primarysections 28, 30 and 32. Spacers 46, 48 and 50 are located on smallersections 34, 36 and 38. I Lugs 17, 18 and 20 fit within apertures 52, 54and 60 and externally threaded ends 62 and 64. The apertures 52, 54 and56 extend through the length of base 58. The lugs are held therein byuse of a cement (not shown) such as an epoxy resin or one of theSauereisen cements. Coupling 66 is tubular and has internal threads 68which engage threads 64 of base 58 and also has internal threads at theother end to which tubular extension 70 attaches by means of threads 72.Guard member 74 is internally threaded to engage threads 62 of base 58and contains test specimens 10 and 12, and common tap 16 within itsinner opening 76. Holes 78 through the wall of guard 74, communicatingwith opening 76, allow ingress and egress of the corrosive atmosphere tothe test specimens.

Figure 2 shows one end of base 58 and the spaced relationship ofapertures 52, 54 and 56. Hexagonal section 60 is, of course, for thepurpose of engaging a wrench thereto to facilitate assembly of thedevice.

In Figure 3, wherein the positioning of plug 17 within aperture 52 ofbase 58' is shown, the sealing action of 0 ring" 40 against the innerwall of aperture 52 is made clear. Aperture 52 has restricted portion 80terminating: in shoulder 82 which, in cooperation with the end ofprimary cylindrical section 28 of lug 17 forms a pressure seal withgasket 84. Cement may be applied between spacer 46 and gasket 84 in theannular space between section 34 and the wallof restricted portion 80.This arrangement prevents blowout of the lugs 17, 18 and 20 due topressure forcing against the exposed body of these lugs and forms aneffective pressure sealwithin base 58L Details of this construction areshown in Figure 4. Shoulder 82 may be angular instead of square asshown.

In Figure the parts shown in Figures 1, 2 and 3 or 4 are assembled andmounted in and through pipe 96 and valve 92 operated by wheel 94. Valve92 may be any type of valve having an opening large enough to receivethe assembled device and adapted to close pas sageway 96 of pipe 90.Pipe 90 is attached to vessel wall 98 as by means of threads 1100 toprovide an open- :ing therethrough for entry of the test specimens,housed to a measuring instrument (not shown).

4 within guard 74, into the corrosive atmosphere confined by wall 98.

The other end of pipe or tubular housing is provided with threads 102 toengage packing gland 104 having tapered inner shoulder 106, opening 108and internal threads 110 at the enlarged end thereof. Packing nut 112engages threads 110 and forces against gasket 114 to form a seal aroundextension 70. Packing nut 112 has opening 116 to permit the entry 'ofextension 70.

The assembly as shown in Figure 5 is mounted and ready for use whenleads 22, 24 and 26 are connected In practice, before the test probe isinserted, valve 92 will be closed. When the probe is to be installed, itis inserted through packing gland 104 with gasket 114 in place untilguard 74 reaches the closed valve 92. Packing nut 112 is drawn up untila seal is provided around extension 70. This seal is sufficient toprevent the escape of corrosive atmosphere during any movement ofextension 70. With the seal by gasket 114 established, valve 92 isopened and the entire assembly is further advanced therethrough until inthe position shown in Figure 5. Valve 92 may then be partially closedaround extension 70 to act as a support and packing nut 112 is tightenedto provide a maximum sealing pressure. 7

At the completion of the use of the instrument, valve 92, which may bean ordinary gate valve is opened fully, the device is withdrawn untilguard 74 clears the valve 92 and valve 92 is closed. Packing nut 112 isthen removed and the device withdrawn from pipe 90.

The various component parts of the test probe as described may be madeof any materials of construction and are preferably made of metal ormetal alloys that are resistant to the corrosive action of theenvironment in which the unit is used. The gaskets and 0 rings used inthe test probe, which are subjected to elevated temperatures, should beconstructed of such insulating and sealing material available that isresistant to corrosion and has good electrical properties. Suitablematerials include Tefion, paper and fabric laminates such as thephenolic and epoxy resin, laminates where the maximum operatingtemperature of the test probe does not exceed about 250 F. Thesematerials, described in Materials and Methods, vol. 42, No. 1, July1955, exhibit good metal bonding strength, flexing strength, and arcresistance, and are of low cost. The maximum temperature at which thesematerials may be joined is about 400 to 450 F. with a time of heatingnot more than about 5 seconds. The maximum operating temperatures forglass fiber laminates are; melamine, 260 F.; silicone, 300 F.;polystyrene, 170 F.; polyester, 250 F.; Teflon 300 F.+; and epoxy 250F.+, but the binding temperatures are higher and the dimension stabilityis improved over paper and fabric laminates. Phenolic nylon fabriclaminates would have only limited application, since the maximumoperating temperature during fabrication or use is only about F. Ceramicinsulators such as titanite, steati'te, glass bonded mica, and glassbonded synthetic mica withstand high temperatures and high frequencies.The latter-named mica inorganic materials can be used or fabricated attemperatures as high as 650 to 750 F.

Test element 12 is coated or protected by a thin layer of a protectivecoating having good insulating and eerrosion resisting properties.Suitable examples of such materials include such proprietary compoundsas Tygon paint (American Chemical Paint Co., Ambler, Pa), Armstrong A-2adhesive; Carbol e'ne Phenoline 300; Scotchcast Resin-MMM? Sauereise'ncement, which is desirable for high temperature applications;fluorinated ethylene polymers such as Kel-F, Teflon, polyethylene (thesewould have to be flame-sprayed); or any corrosion resistant, relativelynon conducting coating, These and other plastic materials ofconstruction are described in detail in Modern Plastics Encyclopedia,vol.

33, No. 1A, 1955, published by Plastics Catalogue Corp. of Bristol,Connecticut. The Plastics Properties Chart accompanying this publicationgives the physical, chemi cal, electrical, molding and other propertiesof numerous plastics, and their trade names, that may be used.

The coating should be of sufficient thickness to provide completeprotection to the coated resistance element both during the test life ofthe corrosion testing unit or probe and during handling or storage. Thecoating may be applied by spraying, dipping, brushing, etc., amenable tothe particular coating chosen.

The test specimens and 12 have substantially the same resisitivty, whichmeans they will have substantially the same chemical composition. Thisis necessary in order that the bridge measuring circuit, which isconnected to the test probe by means of leads 22, 24 and 26, may be madeto function accurately without tedious calibration. However, it isunnecessary that the configuration or total resistance of the protectedand unprotected test specimens be identical. Because thecorrosionmeasuring process with which the test probe of this inventionis used utilizes a comparison method for determining the change inresistance of the unprotected test specimen or resistance element whenexposed to corrosive conditions, the bridge circuit in which the testprobe is installed during use is initially balanced by adjusting theratio of the resistance elements.

The test specimens may be any shape, that is ribbonlike or in a shape ofrods. The test specimens may be fabricated from one piece of thematerial of construction under consideration and the common junction 14formed by welding common lead 16 to a midpoint thereof. Before use orwhen new, the test specimens have substantially the same electricalresistivity and chemical composition. Advantages accrue in constructingthe test specimens or elements from materials having the same resistancevalues. However, suitable unsymmetrical corrosion testing elements canbe fashioned in accordance with this invention in which the resistancesof these elements are not identical, provided, for the sake ofconsistency, a material of construction is employed which issubstantially uniform in composition and resistivity. The ratio of theresistance of the unprotected test specimen to the resistance of theprotected test specimen, expressed as R unprotected R protected may varyfrom values of about 0.1 to 10. When a corrosion test elementcombination is fabricated from test specimens having differentresistances within the above ratios, corresponding changes in the valuesof the resistances of the other branches of the bridge circuit will haveto be made. Although, theoretically, the above ratios of resistancescould vary over wide limits, as a practical matter there are mechanicaland electrical factors which have to be taken into consideration in thedesign of a suitable corrosion testing unit or probe. Lead resistance,for example, will be appreciable if a small corrosion testing probe isused in which the resistance of one element is only about a tenth orless of the resistance of the other element. This factor is notpronounced in the case of large, unsymmetrical test elements in whichthe resistance of even the smaller one is large compared with the leadresistance. Lead resistance can be substantially eliminated by themanner of interconnecting the corrosion testing unit with the bridgecircuit. Mechanical considerations include making the test probe unitlarge enough for easy assembly and attachment of the lead wires, and tooffset an unbalance in temperature compensation.

From this description it is seen that the invention is necessarilyconfined to the use of test specimens having the property of conductingelectricity and showing a change in resistance proportional to changesin cross? sectional area. due to corrosion. The materials ofconstruction that meet these requirements include all metals and metalalloys such as steel, iron, bronze, brass, copper and the like. Theenvironment to be investigated by the test elements or the completedtest probes of this invention may be in any physical state or may existas a mixture of substances in different physical states. The corrosiveenvironment may be gaseous, vaporous, solid, or semi-solid, or a mixtureof these forms of matter. Examples include corrosive gases, such as thehalogens, acid or base solutions, flue gases, and mixtures of gases orcarrier liquids containing a high content of solids, such as catalystparticles. These environments may be considered to be corrosive becauseof their chemical effects and erosive because of their mechanicalefiects on the metal surfaces which result in disintegration thereof orloss of portions of the exposed test specimen. An example of a corrosiveliquid environment would be an acid solution or an ammoniaammoniumnitrate fertilizer solution.

Since the test probe of this invention is designed for use at relativelyhigh pressures and temperatures, care should be exercised in theselection of the materials of construction for the base member andassociate parts. The thread and gasket-sealing surfaces should be care-.fully prepared so as to be without roughness or flaws. Thread-sealingcompounds may be used on the threaded surfaces to insure against leaks.

What is claimed is:

1. A corrosion-test probe mounting comprising, in combination, a basemember adapted to be attached through the wall of a vessel containing acorrosive atmosphere, apertures extending longitudinally through saidbase member, each of said apertures having a circumferential shouldertherein, that portion of the apertures on the pressure side of the basemember being larger than the remainder of each aperture, lug membersmounted within each of said apertures in insulated relationshiptherewith, said lug members having a shoulder portion, an enlargedportion and a constricted portion corresponding to said apertures,circumferential insulating means between the outer wall of said lugmembers and the inner wall of said apertures, circumferential insulatingmembers between the shoulder portion of each of said lug members and thecorresponding shoulder of said apertures, and means for maintaining saidcorrosion-test probe mounting within a corrosive atmosphere.

2. A corrosion-test probe mounting in accordance with claim 1 in whichsaid corresponding shoulder portions have parallel surfaces normal tothe longitudinal axis of said apertures and said lug members.

3. A corrosion-test probe mounting in accordance with claim 1 in whichsaid corresponding shouder portions have parallel surfaces oblique tothe longitudinal axis of said apertures and said lug members.

4. A corrosion-test probe mounting in accordance with claim 1 in whichthe shoulder portions of said aperture are normal to the longitudinalaxis of said apertures and the shoulder portions of said lug members areoblique to the longitudinal axis of said lug members.

5. A corrosion-test probe mounting in accordance with 'claim 1 havingtest specimens attached to two of said lug members and a common leadattached to a third lug member, said points of attachment being at theenlarged pressure side ends of said lug members, said test specimens andsaid common lead being joined at a common juncture.

6. A corrosion-test probe in accordance with claim 5 having a perforatedtubular guard member surrounding and spaced from said test specimens andsaid common lead, said guard member being supported by said base member,electrical leads ttaching to the constricted 'ei hd's of id lugihefilbefs.

, 7. A cqfi'osion-test p'f'bb ih :ic co'rdi'nc with clim 6 iii which atubular eitenion arid Support member enco'thpeisses said leads nd isattached to 'said base 5 member.

I References Cited in the file ofthis patent UNITED STATES PATENTS OTHERREFERENCES The Oil and Gas Journal, November 21, 1955, pages 135-138,AIP Section.

